public class Main {
    public static void main(String[] args) {
        Student student = new Student("张三",28);
        System.out.println();
        Undergraduate undergraduate = new Undergraduate("李四",30,"硕士");
        Circle circle = new Circle();
        System.out.println(circle.area(3));
        Square square = new Square();
        System.out.println(square.area(2));

    }
}
